Question

A galvanometer of resistance 50 ohm which gives a full scale deflection for 1mA is to be adapted to measure currents of up to 5A if this resistor is made of a material of cross sectional area 4×10^-4 and resistivity 2×10^-6. Calculate it's length

Answer 1

$I(R)=I−I(r)=5A−0.001A=4.999A;I(R)\times R=r\times I(r);R=\frac{r\times I(r)}{I(R)}=\frac{50\times 0.001}{4.999}=0.01Ohm;L=\frac{4\times 10^{-4} \times 0.01}{2\times 10^{-6}} = 2m I(R)×R=r×I(r);R= I(R) r×I(r) ​ = 4.999 50×0.001 ​ =0.01Ohm;L= 2×10 −6 4×10 −4 ×0.01 ​ =2m$